1. Field of the Invention
The invention relates to a cutting and transport roller which exhibits an outer shell provided with a slotted opening and containing a cutter for cutting the material webs which rest on the shell of the transport roller. The cutter contains at least one knife, which is guided by a cutter holder and which in turn exhibits at least one cutting edge, the knife being hinged to the cutter holder so as to swivel and reach through the opening in the shell during the cutting process of the material web. The present invention also relates to a process for cutting a material web with the aid of such a roller.
The invention relates to a cutting and transport roller with integrated cutter in accordance with the preamble of claim 1 and a process for cutting a material web with the aid of such a roller.
2. Description of the Related Art
Cutting and transport rollers of the aforementioned kind are known. The EP 0 698 571 A2 shows a cutting and transport roller, which exhibits an outer shell, provided with a slotted opening, and contains a cutter for material webs. Said cutter severs the material webs, resting on the peripheral surface of the transport roller. This cutter exhibits a cutter bar with a knife with a serrated cutting surface.
The cutter bar is hinged to the cutter. During the cutting process of the material webs, resting on the cutting and transport roller, knife and cutter bar execute a translational motion in the radial direction of the cutting and transport roller, whereby at least the knife reaches through the slit in the shell and pierces the film. After the cutting process knife and cutter bar are withdrawn again into the interior of the roller.
Devices of the described type are mechanically complicated, because the forces required to sever the material webs are large. Moreover, after the completed cutting process, knife and cutter bar have to be withdrawn into the interior of the roller, which is rotating in the normal case. In this process the force, generated by the cutter, has to overcome a significant. centrifugal acceleration, which acts on the knife and cutter bar.
The large force, generated by the cutter during the cutting process, is transferred at least partially to the material web and has to be compensated for there, for example, by means of complicated vacuum or suction mechanisms, which are supposed to prevent the material web from being pushed away and then sliding off the roller.
Therefore, the present invention is based on the problem of reducing the mechanical complexity of such a device.
This problem is solved in that the cutter, integrated into the roller, is assigned at least one knife, which is linked to a knife holder so as to swivel, whereby the swivelable coupling of said at least one knife defines for said at least one cutting edge of the knife an axis of rotation, which runs either parallel or at an acute angle to a perpendicular line on the plane, which is defined by the radial (r) and the axial (z) coordinates of the cutting and transport roller.
Owing to these measures, the cutting blades of at least one knife execute during the cutting process a motion, which includes at least rotary components.
The inventive design of a cutting and transport roller has a number of advantages.
For example, during the cutting motion with exclusively rotary components, only said at least one knife, but not the generally heavy cutter bar is moved.
In addition to the simpler mechanical design of the cutting mechanism, the complexity, caused by the necessity to hold the film on the roller according to the state of the art, is also reduced. In a cutting process, which is carried out exclusively by means of a translation of the knife in the radial direction of the roller, the film is also forced outwards exclusively in the radial direction.
In a device, according to the present invention, the cutting knives can be positioned in such a manner that the film is pushed away from the roller only during the first half of the piercing procedure. During this period, the film is only perforated and not yet completely severed. Therefore, the film is held on the roller largely due to its looping around the roller on both sides of the perforation and due to the still existing web tension.
After the rotational motion of the knife blades in the radial direction has surpassed its apex, the rotational motion of the knife acts radially in the direction of the main axis of symmetry of the roller and, in this manner, counteracts a lifting of the material web from the roller. In light of the centrifugal acceleration which acts on this material web when the roller rotates around its main axis of symmetry, this state is very advantageous.
The described advantages still remain, even when translational motion components are superposed on the rotational motion of the present invention. This requirement can be converted mechanically in the radial direction by means of the motion of the cutter bar.
However, in light of the enormous centrifugal forces owing to the high roller speed generated in the interim, a device according to the present invention can also be advantageously provided with vacuum and suction mechanisms, which prevent the material web from being lifted from the roller especially after the cutting process.
Above all, a device according to the present invention can make do with a plurality of knives with very thin blades. Therefore, in a device of this type, economical industrial knives or knives of ground thin sheet steel can also be used.
In a device with a plurality of knives it is advantageous, if the spacing between the knives is less than or equal to the length of the cut, for the knives to be affixed into the material web during the cutting process.
Another possibility to guarantee a complete, clean severing of the web lies in a translation of the cutter, preferably in the axial direction during the cutting process.
If the cutting process is performed by a plurality of knives, the cutting processes are advantageous, wherein the different knives make contact with the material web at different times. In this manner the force or torque complexity of the cutting process is reduced. Advantageous devices to carry out such a process include, for example, knives of varying lengths or knives suspended from points of rotation and that are positioned so as to be offset in the radial direction of the roller.
Another advantageous method for carrying out the process of the present invention can be performed with the aid of a circular cutter, which can be designed similarly to a circular saw. Such a circular cutter advantageously provides a torque with the aid of an electric motor and consequently puts a substantially circular disk-shaped knife into an inventive rotational motion around its main axis of symmetry. To sever wide material webs cleanly over their entire width, the thin substantially circular knife can be moved in the axial direction of the roller.
Other features and advantages of the invention are disclosed in the other dependent claims and the following description in conjunction with the drawings, in which the embodiments of the invention are depicted as schematic drawings.